Some hydraulic systems use a pressure compensated unloading valve to dump the discharge fluid flow from a fixed displacement pump directly to tank when the control valve is in neutral. The unloading valve also maintains pump discharge pressure at a preselected level above the load pressure when one of the control valves is actuated. The unloading valve is shifted to the blocking or pressure compensation position by a positive load signal directed to the load signal chamber thereof from the control valve. One of the problems encountered with such systems is that of slow response of the hydraulic system during at least one operating condition wherein a positive load signal is not present to load up the unloading valve such that it does not move to the fluid blocking position. One such condition exists when a control valve connected to a load supporting hydraulic jack is shifted to lower the load i.e. lower a bucket of a loader. Under the influence of the load, the fluid is forced out of the load supporting end of the hydraulic jack faster than the fluid is directed to the other end such that the unloaded end of the hydraulic jack tends to cavitate. Thus, when the bucket reaches the ground, there is no positive load signal being directed to the unloading valve and its remains in a dump mode so that only a small amount of fluid from the pump is being directed the cavitated end of the hydraulic jack. This causes an undesirable delay or lag in the response time when the control valve is maintained in a position for applying a downward force to the bucket.
The present invention is directed to overcoming the problem as set forth above.